1. Field of the Invention
The present relates to a semiconductor device, such as thermistors, diodes and transistors comprising a diamond thin film.
2. Description of the Prior Art
Diamonds can be made into p-type semiconductors, and since they have advantages such as wide band gap, high carrier mobility, and excellent heat and environmental resistances, their use with semiconductor devices has become increasingly popular.
There are two types of diamond thin film semiconductors:
(1) a device comprising a single crystal diamond substrate having thereon a diamond thin film as the active layer, i.e., a device comprising a homoepitaxially grown active layer of diamond, and
(2) a device comprising a thin film diamond active layer formed on a substrate made of a different material such as Si.
Examples of the homoepitaxially formed diamond device set forth in (1) above include experimentally fabricated Schottky diodes or NESFET's comprising a Schottky junction between a p-type diamond layer epitaxially grown on a single crystal diamond and a tungsten (W) or aluminum (Al) layer. Since an n-type diamond is not yet available, a Schottky junction between a p-type diamond and a metal is presently used.
Examples of the diamond devices found within group (2) above include experimental devices such as thermistors comprising polycrystalline diamond grown on a Si substrate and thin film electroluminescent (EL) devices comprising a polycrystalline diamond layer as the light-emitting layer. Present technology allows single crystal diamond thin films to grow only single crystal diamond substrates. In cases where Si or another metal is used as the substrate, only thin films of polycrystalline diamond are available. Thus, devices categorized as (2) are, without exception, based on polycrystalline diamonds.
In both cases above, however, the prior art technology used direct formation of the active diamond thin film on a substrate, using deposition methods such as microwave plasma CVD (chemical vapor deposition), RF (radio frequency) plasma CVD, ECR (electron cyclotron resonance) plasma CVD, and the like.
The prior art devices described above suffer from the following disadvantages:
(1) poor interface characteristics resulting in devices that provide insufficient characteristics with such characteristics probably being due to the formation of various interface states; and
(2) poor film quality of the active layer formed at the initial stage of deposition, that is the active layer in contact with the substrate is so inferior that the resulting device is far from satisfactory. This is particularly problematic when a active layer as thin as 1 .mu.m or less is required.
These deficiencies manifest themselves more readily when the diamond films are formed on a substrate other than diamonds.